for videography its the best slr around in that price bracket so for your needs its a good step up. As far as i am aware the quality of video and variety of video settings are the reasons of this, however i have very little knowledge of either of those cameras video capabilities.
In terms of photography and what will make better pictures, they will both produce high quality raw files, the MP difference is irrelevant if your not printing large or cropping a lot. i prefer ergonomics of nikon cameras to any other brand in the world (except mamiya but they cannot be compared to cropped digital sensor cameras!) Its really all dependant on lens quality. If i had the money for a 7d and no lens i would buy a second hand d200 or d2x (or keep the d90) or even older system that has half decent 9+ af points and a pro lens. It is widely excepted that cannon make the better of the premium lens however from my personal experience i find lower end lens quality is better from nikon. You can get some old mf lens' on a budget that are just pure quality!
so i would buy the 7d if i had enough money for a nice lens (i would say that a 50 1.8 would suffice but on a cropped body i think it will restrict you heavily)
I would keep the d90 if i only had enough money for a new body and i would buy a nice lens instead.
if you do decide to buy the 7d on a budget i would suggest some of cannons primes like 85 1.8, 50 1.8, 35 1.8 etc as they are not bad if not a little cheaply built. Any cheap zooms and you would have been 100 times better off with your d90.